Conventionally, there is developed a technique for purifying exhaust gas from a diesel engine by disposing an exhaust gas purification device (diesel particulate filter) in an exhaust gas flow path of the engine and by using an oxidation catalyst, a soot filter, or the like of the exhaust gas purification device (see, for example, Patent Document 1, Patent Document 2, or Patent Document 3).
Conventionally, there is a structure in which the exhaust gas purification device is mounted on the engine (see, for example, Patent Document 1 or Patent Document 2), or a structure in which the exhaust gas purification device is disposed separately from the engine (see, for example, Patent Document 3).